With the progress of technology, various kinds of electronic products have been developed in recent years. These electronic products are designed to satisfy people's desire and facilitate people's daily life. These electronic products are made up of a variety of electronic elements with different voltage specifications. Hence, the AC power used in the contemporary power system is not adaptable for use with the electronic products. In order to supply an appropriate voltage for all kinds of electronic elements to operate normally, these electronic products requires the AC power, such as the utility power, to be converted by a power supply into a voltage tailored for the electronic products.
With the awakening of environment protection, the developments of electronic products are following the trend of power saving. The power supplies also have to be featured with low energy consumption. In order to optimize the energy utilization and provide the load with high-reliability and high-current power, it is a popular norm to constitute a power system by connecting a multiplicity of power supplies with the same power rating or different power rating in parallel with each other.
Nowadays, some parallel-connected power supplies of the power system are provided with active current sharing circuits for allowing the current required by the load to be equally distributed among the power supplies by the active current sharing technique with precise current balancing feature. Also, some parallel-connected power supplies of the power system are provided with droop current sharing circuits for allowing the current required by the load to be equally distributed among the power supplies by the droop current sharing technique with simple circuitry, fast response, and invulnerability against oscillation.
The artisan of the power supply industry can readily understand that the active current sharing technique and the droop current sharing technique both have their own advantages. Nonetheless, the power supply employing the active current sharing technique bears the disadvantages of complicated circuitry, slow response, and vulnerability to oscillation. Although the droop current sharing technique can eliminate the disadvantages encountered by the active current sharing technique, the droop current sharing technique can't provide good current balancing effect. Thus, the user has to decide whether the parallel-connected power supplies employing the active current sharing technique or the parallel-connected power supplies employing the droop current sharing technique are to be used to constitute a power system, instead of allowing the user to flexibly adopt the parallel-connected power supplies employing the active current sharing technique and the parallel-connected power supplies employing the droop current sharing technique to constitute a power system.
Furthermore, in order to enhance the reliability of power system, the parallel-connected power supplies of the power system will install an additional redundant power supply to ensure that the redundant power supply can provide backup power for the power system to sustain operation for a period of time when one of the power supplies of the power system is operating abnormally. This technique is called N+1 system. That is, instead of requiring N power supplies to constitute a power system to power the load, the power system needs N+1 power supplies to maintain a smooth operation. However, in order to ensure that the redundant power supply can immediately provide backup power for the power system to sustain operation for a period of time when one of the power supplies of the power system is operating abnormally, the redundant power supply has to keep operating all the time. As the power supply will suffer power loss during operation, the total power loss of the power system will increase as the number of the power supplies installed in the power system is increased. In other words, the power system will suffer excessive power loss as the redundant power supply is required to operate without respite.
Therefore, there is a tendency to develop a power system consisted of parallel-connected power supplies with active current sharing and droop current sharing functionality and the power system assembly using the same. The invention can meet these needs.